Patent GB-796421-A (GB)
Title: Method of reducing aromatic nitrogen compounds
Filed: 1955-08-05
Abstract: Aromatic nitrogen compounds containing nitrogen in a reducible form as a nuclear substituent of a benzene nucleus at a higher stage of oxidation than the hydrazo stage are reduced by reacting the aromatic nitrogen compound with an aldehyde other than a reducing sugar and a caustic alkali in a reaction medium in which a naphthoquinoid reduction promoter has been incorporated.  The naphthoquinoid reduction promoters which may be used in the process include the reduction promoters specified in Specifications 701,128, 716,418, 730,748, 776,716, 780,631 and 780,632 in which the reduction is carried out by metal alcoholates.  Reduction to a lower stage of oxidation than the azoxy stage is facilitated by carrying out the reaction in a medium which contains a water-miscible organic solvent, such as a monohydric alcohol containing not more than 6 carbon atoms per molecule.  The process is particularly useful for the reduction of compounds which contain as nuclear substituents one or more labile halogen atoms.  The aldehyde may be aliphatic, aromatic or heterocyclic and may also be a stabilized form thereof, e.g. paraformaldehyde, or may be used in the form of a compound which reverts to the aldehyde in the alkaline medium, e.g. hexamethylenetetramine.  Specified aldehydes are formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, and furfuraldehyde.  Specified caustic alkalies are sodium and potassium hydroxides.  Specified starting materials are 3-chloronitrobenzene, 2- or 4-nitroanisole, 2-nitrotoluene, 4-nitrobenzoic acid, 2-nitrobenzene sulphonic acid, 2 : 5 - dimethyl - nitrobenzene, 2 - nitrophenetole, 3 : 31 - dimethyl - azoxybenzene, 2 : 21-azoxytoluene, 2 : 21-azoxyanisole, azobenzene, 2 : 21-azotoluene and 2 : 21-azoanisole.  In examples: (1) 2-chloronitrobenzene was reduced in aqueous medium with sodium hydroxide, formaldehyde and 2 : 3-dichloro-1 : 4-naphthoquinone to give 2 : 21-dichloroazoxybenzene; (2) 2 : 21-dichloro-azoxybenzene was reduced in alcoholic medium with sodium hydroxide, formaldehyde and 2 : 3-dichlor-1 : 4-naphthoquinone to give 2 : 21-dichlorohydrazobenzene and some 2-chloro-aniline; (3) 2 : 21-dichloroazobenzene was reduced in a methanol medium as in (2) to give 2 : 21-dichloro-hydrazobenzene and some 2-chloro-aniline; (4) as in (3) but using paraformaldehyde 2 : 21-dichloroazoxybenzene was reduced to 2 : 21-dichlorohydrazobenzene with some 2 : 21-dichloro-azobenzene and 2-chloroaniline; (5) nitrobenzene was reduced in aqueous medium with sodium hydroxide, 2 : 3 - dichloro - 1 : 4 - naphthaquinone and formaldehyde, paraformaldehyde, butyraldehyde, benzaldehyde or furfuraldehyde to give azoxybenzene and some aniline; (6) nitrobenzene was reduced in aqueous medium with sodium hydroxide, formaldehyde and 4a : 5 : 8 : 8a - tetrahydro - 1 : 4 - naphthaquinone to give azoxybenzene and some aniline; (7) nitrobenzene was reduced in methanol medium with sodium hydroxide, formaldehyde and 2 : 3-dichloro-1 : 4-naphthoquinone to give hydrazobenzene; (8) azoxybenzene was reduced in methanol medium with sodium hydroxide, formaldehyde and 2 : 3-dichloro-1 : 4-naphthoquinone to give hydrazobenzene or a mixture thereof with azobenzene; (9) 2-chloronitrobenzene was reacted with methanolic sodium hydroxide to give 2-methoxy-nitrobenzene, further sodium hydroxide and methanol were added together with 2 : 3-dichloro-1 : 4-naphthoquinone and the mixture reacted to form 2 : 21-dimethoxy-azoxy- and -azobenzenes, then paraformaldehyde was added and the mixture further reacted to give 2 : 21-dimethoxy-hydrazobenzene.  The processes of Examples (1)-(3) and (5)-(8) were also carried out without the naphthoquinoid reduction promoter or the aldehyde for comparative purposes.  Specification 796,356 also is referred to.